gdb: arch to tell whether it supports 'g' packets

This adds a callback to gdbarch so indicate whether
the architecture supports 'g' packets to remote target.
For example, on Xtensa, xt-ocd does not support 'g'
packet. However, the register fetching code keeps on
trying 'g' packet which results in infinite loop. So
this provides a mechanism for architecture to indicate
whether 'g' packet is supported.

Signed-off-by: Daniel Leung <daniel.leung@intel.com>
Signed-off-by: Stephanos Ioannidis <root@stephanos.io>

Author: dcpleung

gdb/arch-utils.c

@@ -1130,6 +1130,13 @@ default_update_call_site_pc (struct gdbarch *gdbarch, CORE_ADDR pc)
   return pc;
 }
 
+/* See arch-utils.h  */
+int
+default_remote_supports_g_packet (struct gdbarch *gdbarch)
+{
+  return 1;
+}
+
 /* Non-zero if we want to trace architecture code.  */
 
 #ifndef GDBARCH_DEBUG

gdb/arch-utils.h

@@ -414,4 +414,7 @@ extern enum return_value_convention default_gdbarch_return_value
       struct regcache *regcache, struct value **read_value,
       const gdb_byte *writebuf);
 
+/* Default implementation of gdbarch remote_supports_g_packet method.  */
+extern int default_remote_supports_g_packet (struct gdbarch *gdbarch);
+
 #endif /* GDB_ARCH_UTILS_H */

gdb/gdbarch-gen.c

@@ -261,6 +261,7 @@ struct gdbarch
   gdbarch_read_core_file_mappings_ftype *read_core_file_mappings = default_read_core_file_mappings;
   gdbarch_use_target_description_from_corefile_notes_ftype *use_target_description_from_corefile_notes = default_use_target_description_from_corefile_notes;
   gdbarch_core_parse_exec_context_ftype *core_parse_exec_context = default_core_parse_exec_context;
+  gdbarch_remote_supports_g_packet_ftype *remote_supports_g_packet = default_remote_supports_g_packet;
 };
 
 /* Create a new ``struct gdbarch'' based on information provided by
@@ -533,6 +534,7 @@ verify_gdbarch (struct gdbarch *gdbarch)
   /* Skip verify of read_core_file_mappings, invalid_p == 0.  */
   /* Skip verify of use_target_description_from_corefile_notes, invalid_p == 0.  */
   /* Skip verify of core_parse_exec_context, invalid_p == 0.  */
+  /* Skip verify of remote_supports_g_packet, invalid_p == 0.  */
   if (!log.empty ())
     internal_error (_("verify_gdbarch: the following are invalid ...%s"),
 		    log.c_str ());
@@ -1401,6 +1403,9 @@ gdbarch_dump (struct gdbarch *gdbarch, struct ui_file *file)
   gdb_printf (file,
 	      "gdbarch_dump: core_parse_exec_context = <%s>\n",
 	      host_address_to_string (gdbarch->core_parse_exec_context));
+  gdb_printf (file,
+	      "gdbarch_dump: remote_supports_g_packet = <%s>\n",
+	      host_address_to_string (gdbarch->remote_supports_g_packet));
   if (gdbarch->dump_tdep != NULL)
     gdbarch->dump_tdep (gdbarch, file);
 }
@@ -5529,3 +5534,20 @@ set_gdbarch_core_parse_exec_context (struct gdbarch *gdbarch,
 {
   gdbarch->core_parse_exec_context = core_parse_exec_context;
 }
+
+int
+gdbarch_remote_supports_g_packet (struct gdbarch *gdbarch)
+{
+  gdb_assert (gdbarch != NULL);
+  gdb_assert (gdbarch->remote_supports_g_packet != NULL);
+  if (gdbarch_debug >= 2)
+    gdb_printf (gdb_stdlog, "gdbarch_remote_supports_g_packet called\n");
+  return gdbarch->remote_supports_g_packet (gdbarch);
+}
+
+void
+set_gdbarch_remote_supports_g_packet (struct gdbarch *gdbarch,
+				      gdbarch_remote_supports_g_packet_ftype remote_supports_g_packet)
+{
+  gdbarch->remote_supports_g_packet = remote_supports_g_packet;
+}

gdb/gdbarch-gen.h

@@ -1793,3 +1793,9 @@ extern void set_gdbarch_use_target_description_from_corefile_notes (struct gdbar
 typedef core_file_exec_context (gdbarch_core_parse_exec_context_ftype) (struct gdbarch *gdbarch, bfd *cbfd);
 extern core_file_exec_context gdbarch_core_parse_exec_context (struct gdbarch *gdbarch, bfd *cbfd);
 extern void set_gdbarch_core_parse_exec_context (struct gdbarch *gdbarch, gdbarch_core_parse_exec_context_ftype *core_parse_exec_context);
+
+/* No comment */
+
+typedef int (gdbarch_remote_supports_g_packet_ftype) (struct gdbarch *gdbarch);
+extern int gdbarch_remote_supports_g_packet (struct gdbarch *gdbarch);
+extern void set_gdbarch_remote_supports_g_packet (struct gdbarch *gdbarch, gdbarch_remote_supports_g_packet_ftype *remote_supports_g_packet);

gdb/gdbarch_components.py

@@ -2835,3 +2835,14 @@
     predefault="default_core_parse_exec_context",
     invalid=False,
 )
+
+Method(
+    comment="""
+Return 1 if arch supports 'g' packets
+""",
+    type="int",
+    name="remote_supports_g_packet",
+    params=[],
+    predefault="default_remote_supports_g_packet",
+    invalid=False,
+)

gdb/remote.c

@@ -1893,6 +1893,7 @@ map_regcache_remote_table (struct gdbarch *gdbarch, struct packet_reg *regs)
 {
   int regnum, num_remote_regs, offset;
   struct packet_reg **remote_regs;
+  int remote_supports_g_packet;
 
   for (regnum = 0; regnum < gdbarch_num_regs (gdbarch); regnum++)
     {
@@ -1922,9 +1923,11 @@ map_regcache_remote_table (struct gdbarch *gdbarch, struct packet_reg *regs)
 	     [] (const packet_reg *a, const packet_reg *b)
 	      { return a->pnum < b->pnum; });
 
+  remote_supports_g_packet = gdbarch_remote_supports_g_packet(gdbarch);
+
   for (regnum = 0, offset = 0; regnum < num_remote_regs; regnum++)
     {
-      remote_regs[regnum]->in_g_packet = 1;
+      remote_regs[regnum]->in_g_packet = remote_supports_g_packet;
       remote_regs[regnum]->offset = offset;
       offset += register_size (gdbarch, remote_regs[regnum]->regnum);
     }